The invention resides in a vacuum die-casting machine which includes a mold with two mold halves forming therebetween a cavity which is in communication with a casting chamber to which molten metal is supplied from a holding oven.
EP 0 790 090 discloses a vacuum die casting machine. which comprises a casting mold formed by two mold halves for receiving a metal melt. One of the mold halves is stationary and the second mold half is movable in the direction toward the stationary mold half. One of the mold halves is provided with a seal rope at the front edge thereof which extends between the mold halves so as to form a pressure-tight seal between the two mold halves. The casting cavity between the two mold halves is in communication with a casting chamber in which A casting piston is movably supported. The casting chamber is connected via an intake ripe to a warm-holding oven in Which a metal melt is contained. The casting cavity between the mold halves which forms the casting chamber is connected is na intake, pipe to a warm-holding oven in which a metal melt is contained. The casting cavity between the mold halves which forms the casting mold is connected to an evacuation arrangement for generating a vacuum which results in drawing metal melt out of the warm holding oven via the intake line into the casting chamber.
During the procedure of closing the mold halves, care must be taken that no gas from the mold cavity enters the metal melt via the casting chamber and the intake pipe since this would result in undesirable gas inclusions in the melt and a deterioration of the quality of the work piece being cast. In accordance with EP 6 790 090 B1, in order to avoid gas flow into the warm-holding oven during the closing process, the casting piston is used as blocking valve and is moved into a position in which the communication connection with the warm holding oven via the intake pipe is interrupted. To this end, the casting piston is disposed between the casting cavity and the discharge end of the intake pipe. The increased volume in the casting cavity may at the same time be vented to the atmosphere by opening a valve or it may be evacuated via the evacuation arrangement.
It is the principal object of the present invention to avoid gas inclusions in the melt of a vacuum casting machine by simple means.